1. Field of the Invention
The invention relates to thread tensioning devices in general, and more particularly, to adjustable thread tensioning devices having particular application on sewing machines for controlling the tension in needle thread.
2. Description of the Prior Art
Adjustable thread tensioning devices for use in controlling the tension in needle thread on a sewing machine are well known. Such devices generally include a plurality of discs which apply friction to thread extending between them. The discs are spring biased toward one another and the spring tension is adjustable by mechanism which an operator controls by adjusting a dial or the like. Examples of such devices are disclosed in U.S. Pat. No. 3,667,414 issued June 6, 1972, U.S. Pat. No. 4,141,306 issued Feb. 27, 1979, and U.S. Pat. No. 4,180,006 issued Dec. 25, 1979, all of which are assigned to the same assignee as the present application. The prior art devices of this type are complex in construction, difficult to assemble and costly to produce, both because of use of the multiple tension applying discs, and the arrangements employed to effect initial adjustments in these devices as at the time of their installation on a sewing machine.
It is a prime object of this invention to provide an improved needle thread tensioning device which is simple in construction, easy to assemble, inexpensive to produce, and convenient to initially adjust as required to provide the control range desired for the device.
Other objects and advantages of the invention will become apparent during a reading of the specification taken in conjunction with the accompanying drawings.